tdesktop/Telegram/SourceFiles/rpl/combine_previous.h

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/*
This file is part of Telegram Desktop,
the official desktop application for the Telegram messaging service.
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For license and copyright information please follow this link:
https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
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*/
#pragma once
#include <rpl/producer.h>
#include "base/optional.h"
namespace rpl {
namespace details {
class combine_previous_helper {
public:
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template <typename Value, typename Error, typename Generator>
auto operator()(
producer<Value, Error, Generator> &&initial) const {
return make_producer<std::tuple<Value, Value>, Error>([
initial = std::move(initial)
](const auto &consumer) mutable {
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auto previous = consumer.template make_state<
base::optional<Value>
>();
return std::move(initial).start(
[consumer, previous](auto &&value) {
if (auto &exists = *previous) {
auto &existing = *exists;
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auto next = std::make_tuple(
std::move(existing),
value);
consumer.put_next(std::move(next));
existing = std::forward<decltype(value)>(
value);
} else {
*previous = std::forward<decltype(value)>(
value);
}
}, [consumer](auto &&error) {
consumer.put_error_forward(std::forward<decltype(error)>(error));
}, [consumer] {
consumer.put_done();
});
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});
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}
};
template <typename DefaultValue>
class combine_previous_with_default_helper {
public:
template <typename OtherValue>
combine_previous_with_default_helper(OtherValue &&value)
: _value(std::forward<OtherValue>(value)) {
}
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template <typename Value, typename Error, typename Generator>
auto operator()(producer<Value, Error, Generator> &&initial) {
return make_producer<std::tuple<Value, Value>, Error>([
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initial = std::move(initial),
value = Value(std::move(_value))
](const auto &consumer) mutable {
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auto previous = consumer.template make_state<Value>(
std::move(value));
return std::move(initial).start(
[consumer, previous](auto &&value) {
auto &existing = *previous;
auto next = std::make_tuple(
std::move(existing),
value);
consumer.put_next(std::move(next));
existing = std::forward<decltype(value)>(value);
}, [consumer](auto &&error) {
consumer.put_error_forward(std::forward<decltype(error)>(error));
}, [consumer] {
consumer.put_done();
});
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});
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}
private:
DefaultValue _value;
};
template <typename DefaultValue>
combine_previous_with_default_helper<std::decay_t<DefaultValue>>
combine_previous_with_default(DefaultValue &&value) {
return { std::forward<DefaultValue>(value) };
}
} // namespace details
inline auto combine_previous()
-> details::combine_previous_helper {
return details::combine_previous_helper();
}
template <typename DefaultValue>
inline auto combine_previous(DefaultValue &&value) {
return details::combine_previous_with_default(
std::forward<DefaultValue>(value));
}
} // namespace rpl